1. Field of the Invention
This invention relates to electric lamps and has particular reference to an improved base for incandescent lamps and similar devices.
2. Description of the Prior Art
As is well known, the bases used on general lighting type incandescent lamps are provided with a glass insulator which has a sheet metal eyelet embedded in its outer end. The flat circular portion of the eyelet is exposed at the end face of the insulator and serves as the end terminal or contactor for the lamp. A medium-screw type base having such an insulator and eyelet is disclosed in U.S. Pat. No. 2,993,192 issued July 18, 1961, to R. W. Mouat. Another base of this type having an eyelet with a central portion that is dished inwardly to rigidify the sheet metal is disclosed in U.S. Pat. No. 2,987,696 issued June 6, 1961, to H. L. Rudler et al.
While the exposed circular portion of the eyelet in such prior art bases served satisfactorily as an end contact for the lamp, experience has shown that when the fabricated bases are shipped in bulk from the parts factory to the lamp plant (or from the base-making machine to the lamp-making machine in the same plant) the exposed peripheral edges of the eyelets frequently become snagged and are bent outwardly so that the eyelet is "lifted" from the insulator. This defect also occurs during base processing operations before or during lamp manufacture.
Bases with recessed end contacts are known in the art, as evidenced by U.S. Pat. No. 905,478 issued Dec. 1, 1908, to A. Swan, and U.S. Pat. No. 1,460,246 issued June 26, 1923, to H. Hubbell. However, these recessed end contacts were constructed by anchoring a flat metal disc in a previously formed circular recess in the end of the insulator. Thus, the attachment of the contactor disc to the insulator was accomplished by means of a separate time-consuming operation. The added cost and manufacturing difficulties inherent in such an operation make bases of this construction impractical and incompatible with the high-speed mass production techniques employed throughout the industry today.